In order to determine the condition of a patient, and to minimize the diseased state, the need for a rapid diagnosis and appropriate treatment by health care professionals is apparent. Diagnosis of many conditions can be facilitated through the determination or quantitation of antibodies, antigens, nucleotide fragments, and other analytes from a biological specimen, which are indicative of a particular disease state or condition. A rapid, sensitive, specific, and simplistic assay is extremely useful for emergency situations, field testing, physicians' offices and in home diagnostics. As diagnostic tests become more simple and easier to perform, they are being performed away from the professional clinical laboratory setting to physicians' offices and even to the home, where untrained or poorly trained individuals perform the tests, usually following product insert instructions alone. These assays are useful, provided they are performed properly and are safe to handle for the user. Assays that require multiple steps, have multiple reagents, and have limited storage conditions are prone to misuse, especially if they are performed by individuals without adequate training or skills.
Many types of ligand receptor assays have been developed and commercialized. These assays are less expensive if capital equipment can be eliminated, such as scintillation counters, fluorometers, and colorimeters in the case of radioimmunoassay, fluorescent immunoassay, and enzyme immunoassay respectively. Non instrumental assays, such as latex agglutination, enzyme immunoassays on strips, tubes, membrane or filters have increased the usefulness and ease of performance of immunodiagnostic testing, but are still cumbersome requiring washing steps, multiple reagent additions and usually refrigerated storage conditions.
In some assays amplification or growth of viruses and bacteria are desirable before testing to increase the sensitivity of detection. In other assays adsorption steps to remove interferring substances or inhibitors of the ligand receptor assay, or long incubation of reagents are necessary to perform an assay. Each step for an assay increases the difficulty of testing for the minimally trained individual and any device that would reduce user error would improve diagnostic testing.
Horrisberger et al (J. Histo Cytochem volume 25: 295-305, 1977) described the use of colloidal gold particles in an immunoassay. Leuvering in U.S. Pat. No. 4,313,734 also describes such an immunoassay. Cerny in PCT/US patent application number 85/02534 describes a solid phase diffusion assay using gold sol particles as an immunolabel which can be visualized by the naked eye on a capture membrane, and requires no washing step. Bernstein et al (86th annual American Society for Microbiology Meeting, 1986) presented and described a rapid immunodiffusion enzyme labeled antibody assay for Group A streptococci on a membrane in which there is no washing step. Gould and Zuk in U.S. Pat. No. 4,552,839 describe the use of colored or dyed beads in a solid phase immunoassay. Through the introduction of colored immunolabelled binding reagents (i.e. gold sol particles, dyed particles, dye encapsulated liposomes, etc.) and the removal of washing steps it becomes possible to perform receptor ligand assays in a closed system with the sequential additions of all reagents within that system.
A number of antigens of interest in the diagnosis of infectious disease are collected with a sterile swab on a shaft to remove the organisms from the suspected infected area or test site (wounds, lesions, blood, tissues, pus, fluids, etc.). The swab is generally used to transfer organisms to a suitable media for culturing which may take as long as 48 hours for growth of bacteria, and 2 weeks for viruses. If the organisms are viable and do grow, then their identification could be made by biochemical, morphological or immunological methods. This time consuming method is slowly becoming replaced by more rapid immunological testing methods or DNA probe methodologies.
In many immunoassays that utilize a swab for collection of antigens or cells, the swab is placed in a solution to release the antigenic materials or cells after collection. It may be necessary to use enzymes, acids, detergents, etc. to solubilize or breakdown the antigens to expose antigenic determinants. The extracted material can then be used in an immunoassay by removing the fluid from the swab and mixing it with other reagents or adding the other reagents directly to the swab extract. In the case where membrane or filters are used to capture the immunoreactants, it is necessary to bring the fluid containing the immunoreactants in contact with the filter or membrane.
In addition, where extraneous cells or debris may interfere with an assay, it may be necessary to have a prefilter (larger pore size filter or membrane) present between the swab and the capture membrane or capture filter to retain these unwanted components.
In some assays, where antigen expression may be low, amplification can be achieved if the organisms are first cultured and then tested. If the culturing and the testing could be performed in a single device, then testing would be simplified. In some assays where there are inhibitors, cross reactive products, or clotting factors, red blood cells, etc., it may be necessary to add adsorbant materials (i.e. beads, kaolin, antibody coated particles, antigen coated particles, or lectin coated particles), anticoagulants, or buffers etc. before the ligand receptor assay can be performed.